In the ninth century, there was such a high demand for slaves in the Islamic caliphate that a slave’s price rose greatly, one source suggesting that prices reached as high as six hundred thousand dirhams. A century later, however, there appears to have been so much of a surplus that slaves would sell for no more than twenty or thirty dirhams each. Clearly, the ninth century was the heyday of the slave trader, and that is why it became such a popular business venture for the Vikings.